There is ample and alarming evidence from the US, Canada, and Western Europe of the increasing prevalence of injection, rather than smoking, in the use of crack-cocaine. The emergence of crack injection has enormous public health implications for the spread of HIV and other blood-borne pathogens prevalent among IDUs, including HIV, HBV, HCV, and HTLV's. However, like many patterns in drug abuse that emerge outside the purview of their existing surveillance systems the composition of injection groups and injection settings in which crack injection is becoming prevalence has yet to be systematically described. Moreover, the behavioral practices used to prepare and inject crack-based drug solutions have not been evaluated in relation to their effects in exacerbating or attenuating risk for transmission of blood-borne pathogens such as HIV. In previous research, the investigators developed a methodology for characterizing heroin injection practices. Employing techniques of direct observation, the investigators developed a typology of heroin injection practices and demonstrated the independent effects of individual, group, and environmental factors in injection risk practices. Observational data were subsequently used to model laboratory experiments in which a sensitive micro culture assay was used to assess the effects of specific heroin preparation and injection practices on the transmission of HIV-1. In this application, the investigators propose to extend their integration of ethnography and virology in order to describe the emergence of crack injection. The proposed research will be conducted by ethnographers experienced with drug-using populations in a total of eight field sites across the United States and Canada (Atlanta, Bridgeport, Chicago, Los Angeles, New York, San Francisco, Toronto, and Washington, DC). Virological studies will be conducted in the laboratories of Yale University. The investigators will develop a standardized, multi-site ethnographic methodology with which to conduct qualitative research on emerging behavioral practices associated with injection of crack-based drug solutions. Using this methodology, the investigators will describe the physical settings and injection groups in which crack injection practices are prevalent: crack injectors' rationales for employing injection as a mode of administration (with a particular emphasis on the antecedents to the initiation of crack injection); and the full range of behavioral practices used to prepare and inject crack-based drug solutions, including the application of heat, selection of acids for dissolving crack, exposure time in acidic environments, and transmission risks related to binge injecting. As in their prior collaboration with laboratory investigations of HIV transmission, ethnographic data will be used to model laboratory experiments that will assess the effects of crack preparation and injection practices on the transmissibility of HIV-1. Ethnographic data and results of laboratory studies will be used to develop a curriculum for training public health practitioners on risk reduction messages and strategies for crack injectors.